This invention relates to a high nitrogen containing triazine-phenol-aldehyde (T-P-A) condensate which has a low melt viscosity.
The high nitrogen, e.g., 15%-23%, condensate of this invention is an effective curing agent and also provides fire-retardant properties to epoxy compositions. The low melt viscosity of the condensate affords reduced viscosity solutions with better wetting of re-enforcement materials such as glass cloth and fiber, thereby providing composites, e.g., laminates, for printed wire boards with superior properties. The condensate of this invention is also suitable in the manufacture of molded products as well as for other uses enjoyed by phenolic novolac resins.
As flame-retardants for epoxy as well as other resins, addition-type flame retardants such as low molecular weight halides, antimony trioxide and phosphorus compounds are often used. However, such addition type flame-retardants not only adversely influence the properties of the resins to which the flame retardants are added but can cause problems due to their toxicity. More recently halogenated polyhydroxystyrene as well as certain triazine-phenol-aldehyde (T-P-A) condensates have been described as flame retardant additives for epoxy resins. However, the halogenated polymers give off hydrogen halides during a fire whereas the T-P-A condensates have a number of shortcomings.
A major shortcoming of the prior art T-P-A condensates is their high melt viscosity and low nitrogen content. Illustratively, T-P-A condensates used as flame retardants with epoxy resins in both U.S. Pat. Nos. 5,955,184 and EP 0877040 B1 have melt viscosities which are significantly higher than those of the instant invention and nitrogen contents which are below those of the instant invention.
In one aspect, this invention is directed to the preparation of a triazine-phenol-aldehyde (T-P-A) condensate which has a melt viscosity of less than about 2,000 cps at 175xc2x0 C. and contains at least 15% by weight of nitrogen. Such a novel condensate can be prepared by any one of the following four methods.
(1) A first method referred to herein as the high basicity amine catalyst method which comprises the following:
(a) Charging to a reaction vessel, a triazine, about 6 to 12 moles of a phenol for each mole of triazine, from about 0.1% to 2% of a secondary or tertiary amine having a pK basicity of at least 10, and about 2.2 to 3.5 moles of formaldehyde for each mole of triazine to form a reaction mixture. The quantity of the amine is based on the weight of phenol charged to the reaction mixture.
(b) Heating the reaction mixture at a temperature of about 40xc2x0 C. to about 120xc2x0 C. until the reaction mixture is substantially free of formaldehyde wherein the triazine is a member selected from the group consisting of melamine, a mixture of melamine with benzoguanamine wherein the quantity of benzoguanamine is not more than about 50% by weight of the mixture, a mixture of melamine and acetoguanamine wherein the quantity of acetoguanamine is not more than about 50% by weight of the mixture, and a mixture of melamine, benzoguanamine, and acetoguanamine wherein the quantity of benzoguanamine is not greater than about 35% by weight of the mixture, the acetoguanamine is not greater than about 35% by weight of the mixture and the melamine is at least 50% by weight of the mixture, wherein said phenol is a member selected from the group consisting of phenol itself, an alkyl phenol wherein the alkyl has from 1 to 4 carbon atoms substituted in the meta-position of the phenol, a meta-substituted alkoxy phenol having from 1 to 4 carbon atoms in the alkoxy group, and a mixture of phenol itself, the meta-substituted alkyl phenol and the meta-substituted alkoxy phenol; and
(c) after reaction of substantially all of the formaldehyde, heating the reaction mixture at a temperature of at least about 100xc2x0 and reacting phenol in the reaction mixture until reaction of the phenol is substantially completed.
(2) A second method is referred to herein as the low basicity amine catalyst method.
(a) This method charges to a reactor the same quantities of triazine, phenol, formaldehyde and amine as in method (1) above to form a reaction mixture but the amine catalyst has a pK basicity value of less than 10 and the reaction mixture is heated at a temperature of about 40xc2x0 C. to 80xc2x0 C. to react the formaldehyde.
(b) After the reaction mixture is substantially free of formaldehyde an acid having a pK acidity value of about 0.5 to 3.8 in an amount of about 2% to 4% by weight of the reaction mixture is added to the mixture in those instances wherein the reaction mixture does not contain at least 1.5% by weight of the triazine reactant of benzoguanamine and/or acetoguanamine. When the triazine charge contains such quantity of benzoguanamine and/or acetoguanamine such acid addition is not needed. The reaction mixture is then heated at a temperature of at least about 100xc2x0 C. until reaction of the phenol is substantially completed.
(3) A method referred to herein as the low temperature acid catalyst method.
(a) This method uses the same quantities of triazine, phenol and formaldehyde as in methods (1) and (2). Instead of an amine catalyst, the catalyst is that of an acid in a quantity of about 0.05% to about 0.3%, based on the weight of phenol, wherein the acid has a pK acidity value of about 0.5 to 3.8.
(b) The aldehyde content in the reaction mixture is reacted at a temperature of not higher than about 80xc2x0 C., e.g., from about room temperature when the catalyst is formic acid or the phenol is liquified with water or formalin. Preferably the reaction mixture is heated at a temperature of not higher than about 80xc2x0 C. such as that of about 40xc2x0 C. to about 70xc2x0 C. until the mixture is substantially free of aldehyde. After the reaction mixture is substantially free of aldehyde, about 2.0% to 4.0% by weight of the reaction mixture of an acid having a pK acidity of abut 0.5 to 3.8 is added to the reaction mixture, at a temperature of the reaction mixture of not higher than about 80xc2x0 C. such as that of about 50xc2x0 C. to 80xc2x0 C. and preferably at a temperature of about 50xc2x0 C. to about 70xc2x0 C.
(d) The temperature of the reaction mixture is then raised to at least about 100xc2x0 C. until reaction of the phenol is substantially complete.
(4) A fourth method is referred to herein as the high temperature acid catalyst method.
(a) The same quantities of triazine and phenol as in the previous three methods are charged to a reactor to form the reaction mixture. However, about 0.2% to 2% of an acid catalyst having a pK acidity of about 0.5 to about 3.8 is charged to the reaction mixture as well as only about one half of the total amount of the total quantity of 2.2 to 3.5 moles of formaldehyde for each mole of triazine.
(b) The reaction mixture is heated at a temperature of about 70xc2x0 C. to 110xc2x0 C. until the mixture is substantially free of formaldehyde.
(c) After the reaction mixture is substantially free of formaldehyde, the reaction mixture is heated to a temperature of about 120xc2x0 to 160xc2x0 C. for about 0.5 to 2.5 hours.
(d) The reaction mixture is then cooled to a temperature which does not exceed about 110xc2x0 C. such as that of about 80xc2x0 C. to 110xc2x0 and the remainder of the formaldehyde is added;
(e) The reaction mixture is then heated to a temperature of above about 120xc2x0 C. until reaction of the phenol is substantially complete.
In place of the aldehyde being substantially all formaldehyde, the above methods also comprise the substitution of up to about 20 mole percent of the formaldehyde with an equal molar quantity of another aldehyde.
In another aspect, this invention is directed to the condensate prepared by the above described methods.
In still another aspect, this invention provides a composition comprising a high (at least 15%) nitrogen containing triazine-phenol-aldehyde (T-P-A) condensate with melt viscosity up to about 2,000 cps at 175xc2x0 C. and a solubility at about 25xc2x0 C. of at least 80% by weight by the 90:10 methanol:water solvent method.
In yet another aspect, this invention provides a method for lowering the melt viscosity of any T-P-A condensate by physically mixing a T-P-A condensate with from about 0.5% to 20% by weight of benzoguanamine and/or acetoguanamine as well as the compositions prepared therefrom.
In yet another aspect of this invention, the triazine-phenol-aldehyde condensate of this invention either alone or in admixture with another epoxy curing agent and/or another fire-retardant can be used as a fire-retardant curing agent for epoxy resins.
In another aspect, this invention provides a prepreg of a porous substrate comprising a curable epoxy resin and a T-P-A condensate of this invention as the curing agent alone or in combination with another curing agent.
In another aspect, this invention is directed to a laminate comprising a plurality of prepregs impregnated with an epoxy resin and a T-P-A condensate of this invention alone or together with another curing agent wherein the epoxy resin composition is cured.
In another aspect, this invention is directed to curable epoxidized compositions of the T-P-A condensate of this invention.
The Phenol Monomer
The phenol monomer, also, simply referred to as a phenol can be phenol itself, a meta-alkyl phenol having from 1 to 4 carbon atoms, a meta-alkoxy phenol having from 1 to 4 carbon atoms and mixtures thereof. Illustrative of a phenol there can be mentioned: phenol itself; meta-cresol; 3-ethyl phenol; 3-isopropyl phenol; 3-methoxy phenol; 3-ethoxy phenol; etc. Phenol itself is the preferred phenol monomer. The quantity of a phenol charged to the reactor in the manufacture of the condensate of this invention is from about 6 to 12 moles of a phenol for each mole of triazine. Preferably, 7 to 10 moles of a phenol are charged for each mole of the triazine. Also preferred is a mixture of at least 90% by weight of phenol itself and not more than 10% by weight of the alkyl phenol, alkoxy phenol and mixtures of the alkyl phenol and alkoxy phenol. The quantity of phenol charged to the reactor is much greater than the amount which reacts in the formation of the condensate so that free, unreacted, phenol is typically distilled out of the reaction mixture after completion of the reactions.
The Triazine Monomer
The triazine monomer can be: (a) melamine; (b) a mixture of melamine and benzoguanamine wherein the quantity of melamine is at least 50% by weight of the mixture and the benzoguanamine is from about 0.5% to not more than about 50% by weight of the mixture and preferably wherein the amount of benzoguanamine is from about 1% to not more than about 25% by weight of the mixture; (c) a mixture of melamine and acetoguanamine wherein the quantity of melamine is at least 50% by weight of the mixture and the acetoguanamine is from about 0.5% to not more than about 50% by weight of the mixture and preferably wherein the acetoguanamine is from about 1% to not more than 25% by weight of the mixture and the remainder is melamine; and (c) a mixture of melamine, benzoguanamine and acetoguanamine wherein the benzoguanamine is not more than about 35% by weight of the mixture, the acetoguanamine is not more than 35% by weight of the mixture and the quantity of melamine is at least 50% by weight of the mixture and particularly wherein the benzoguanamine and acetoguanamine combined are not more than 25% by weight of the mixture and the melamine is at least 75% by weight of the mixture.
The Aldehyde Monomer
The aldehyde monomer is preferably formaldehyde. However, up to about 20 mole % and preferably up to about 10 mole % of the formaldehyde can be replaced with other aldehydes. Illustrative of other aldehydes there can be mentioned: acetaldehyde, i-butyraldehyde, benzaldehyde; acrolein, crotonaldehyde and mixtures thereof. The term xe2x80x9caldehydexe2x80x9d herein includes not only the aldehydes themselves, but also compounds yielding aldehydes, e.g., paraformaldehyde, trioxymethylene, paraldehyde and the like. The aldehyde may be introduced neat or as a 20% to 50% solution in phenol to facilitate metering in the reaction mixture. However, the formaldehyde is generally charged to the reaction mixture as 50% formalin. Formalin generally contains small quantities of formic acid with about 0.03% of formic acid being typical in a 50% formalin solution.
The quantity of aldehyde used in manufacture of the condensate of this invention varies from about 2.2 to 3.5 moles and particularly about 2.5 to 3.0 moles for each mole of the triazine charged to the reactor.
The Amine Catalyst
The amine catalyst can be a secondary or tertiary amine.
The quantity of amine catalyst, also referred to as a catalytically effective quantity of amine catalyst, will typically vary from abut 0.1% to abut 2% based on the weight of the phenol charged and preferably about 0.25% to 1%.
In the high basicity amine catalyst method, the amine will have a pK basicity of at least 10 such as that of 10 to 11.5. In the low basicity amine catalyst method, the pK basicity will be less than 10 such as about 7 to 9.
Illustrative of aliphatic, cycloaliphatic, and heterocyclic amines having a pK basicity of 10 or more which can be used in this invention, there can be mentioned the following. Tertiary amines of the formula R3N wherein each R is selected from alkyl having one to seven carbon atoms and wherein the nitrogen can be part of a heterocyclic ring. In this regard, each of the alkyl groups can be the same or different. Illustrative of specific tertiary amines, the following can be mentioned. Triethylamine which has a pK basicity of 10.72, tributylamine which has a pK basicity of 10.3, various N-lower alkyl piperidines wherein the alkyl group has from 1 to 4 carbon atoms, e.g., N-ethyl piperidine which has a pK basicity of 10.45, 2-di(n-butylamino)ethanol which has a pK basicity of 9.8, 2-di(isopropylamino) ethanol which has a pK basicity of 9.8, N-methylpyrrolidine which has a pK basicity of 10.32, and N,N-dimethyl cyclohexylamine which has a pK basicity of 10.72.
Illustrative of secondary amines having a pK of 10 or more there can be mentioned: various secondary amines of the formula R1R2NH wherein each R is alkyl of 2 to 4 carbon atoms, e.g., diethylamine which as a pK basicity of 11.05, di-n-butylamine which has a pK basicity of 11.25 and diisopropylamine which has a pK basicity of 11.3; piperidine which has a pK basicity of 11.12; and pyrrolidine which has a pK basicity of 11.32.
Illustrative of amines having a pK basicity of less than 10 there can be mentioned: N-methylmorpholine which has a pK basicity of 7.13; N-methyl diethanolamine which has a pK basicity of 8.52; triethanolamine which has a pK basicity of 7.76; N,Nxe2x80x2-dimethylpiperazine which has a pK basicity of 8.54; 4-methylpyridine which has a pK basicity of 6.03; 2,4-dimethylpyridine which has a pK basicity of 6.77; N,N-diethylaniline which has a pK basicity of 6.61; and N,N-dimethylbenzylamine which has a pK basicity of 9.02.
The Acid Catalyst
The methods of this invention for manufacture of the T-P-A condensate, except the high basicity amine catalyst method (i.e., wherein an amine with a basicity of 10 or greater is used), may use an acid which has a pK acidity value of about 0.5 to about 3.8. The preferred acids with this acidity value are oxalic, formic, and trifluoroacetic acid since they are easily removed from the reaction mixture, particularly in removal of water and the free phenol from the reaction mixture on completion of the condensation reactions. Other acids having the same acidity value such as lactic acid can be used but they can be difficult to remove from the reaction mixture since they do not distill out or decompose as easily.
In the case of oxalic acid as catalyst in the various methods of this invention, the temperature of the reaction mixture is raised above about 130xc2x0 C. such as up to about 170xc2x0 C. together with distillation and preferably when the temperature is raised to about 140xc2x0 C. to about 160xc2x0 C. so that the oxalic acid catalyst is decomposed to volatile components. Oxalic acid can be used in its various forms such as the pure compound, the dihydrate, or mixtures thereof, all of which are referred to as oxalic acid herein.
The Methods for Preparation of the T-P-A Condensate
In both acid processes for making the condensate, the pH of the mixture of phenol, aldehyde, and acid catalyst is less than 2.5 and generally less than 2. Addition of triazine buffers the pH to about 6 to 7 whereas by the addition of an amine catalyst in the absence of triazine, the pH is buffered by the large presence of phenol.
The various reaction steps for preparation of the condensate of this invention are generally conducted in the same reactor. An inert atmosphere, e.g., nitrogen, is optimally employed to minimize oxidation of aldehyde and discoloration of product. In the order of charging ingredients to the reactor, the aldehyde is typically added after the triazine, phenol and catalyst except in the low temperature acid catalyst method when it need not be added after the other ingredients. In each of the methods for the manufacture of the T-P-A condensate, when aldehydes other than formaldehyde are used, such other aldehydes are typically reacted at a temperature of not higher than about 100xc2x0 C. prior to the addition of formaldehyde.
As mentioned hereinabove in the Summary of the Invention, applicant can prepare the T-P-A condensate by four different methods. In all of the methods, the molar ratio of the reactants is the same, namely, charging to a reactor, a triazine, about 6 to 12 moles of a phenol for each mole of triazine, and about 2.2 to 3.5 moles of aldehyde for each mole of triazine.
In the case of both the high basicity amine catalyst method wherein the pK basicity of the amine is at least 10 and the low basicity amine catalyst method wherein the basicity of the amine catalyst is less than 10, from about 0.1% to about 2% of the amine catalyst and preferably from about 0.25% to 1% of amine catalyst, based on the weight of phenol, is charged to the reaction mixture. In both methods, the amine is a secondary or tertiary amine.
The High Basicity Amine Catalyst Method
In the high basicity amine catalyst method, the amount of triazine, phenol and aldehyde charged in the reaction mixture are the same as in all the other methods of this invention for manufacture of the T-P-A condensate. The catalyst has a pK basicity of at least 10. After the ingredients have been charged to the reaction mixture, the mixture is heated at a temperature of about 40xc2x0 C. to 120xc2x0 C. and preferably from about 45xc2x0 C. to about 85xc2x0 C. until the reaction mixture is substantially free of aldehyde, i.e., the aldehyde has reacted. Following this step, the reaction mixture is heated at a temperature of at least 100xc2x0 C., e.g., from about 100xc2x0 C. to about 160xc2x0 C. and preferably from about 110xc2x0 C. to about 140xc2x0 C. Until the phenol has substantially completely reacted, which typically takes about one to four hours.
The Low Basicity Amine Catalyst Method
In the low basicity amine catalyst method wherein the amine has a pK basicity of less than 10 such as about 7 to 9, the reaction mixture is heated at a temperature of about 40xc2x0 C. to 80xc2x0 C. and preferably about 50xc2x0 C. to 70xc2x0 C. Raising the temperature after reaction of the formaldehyde causes the reaction mixture to gel or produce a T-P-A condensate having a melt viscosity of more than 2,000 cps at 175xc2x0 C. unless the triazine reactant includes at least 1.5% of benzoguanamine or acetoguanamine. To prevent the gelation or formation of an unacceptably high viscosity product, a small quantity of an acid having a pK acidity of about 0.5 to 3.8 is added to the reaction mixture at a reaction mixture temperature of not greater than about 80xc2x0 C. Preferably, the reaction mixture is at temperature of about 40xc2x0 C. to 80xc2x0 C. and particularly at a temperature of about 50xc2x0 C. to 80xc2x0 C. at the time the acid is added. The quantity of such acid is about 2% to about 4% based on the weight of the reaction mixture. After the addition of the acid, the reaction mixture is heated at a temperature from about 80xc2x0 C. to about 160xc2x0 C. and preferably from about 100xc2x0 C. to about 140xc2x0 C. until the phenol has completely reacted in the reaction mixture.
The Low Temperature Acid Catalyst Method
In the case of the low temperature acid catalyst method, the initial reaction mixture includes an acid catalyst having a pK acidity of from about 0.5 to about 3.8 wherein the quantity of acid varies from about 0.05% to 0.3% based on the quantity of phenol charged. The quantities of triazine, phenol and aldehyde are the same as the high basicity amine catalyst method and the low basicity amine catalyst method. The aldehyde is charged to the reaction mixture and the reaction mixture is preferably heated at a temperature of about 40xc2x0 to 80xc2x0 C. and particularly at a temperature of about 45xc2x0 C. to about 60xc2x0 C. until the reaction mixture is substantially free of aldehyde. However the reaction of the aldehyde in this method can take place at a lower temperature range such as that of about 25xc2x0 C. or slightly below when formic acid is the catalyst. After the reaction mixture is substantially free of aldehyde, an acid having a pK acidity of about 0.5 to about 3.8 in an amount of from about 2% to 4% of the reaction mixture is added to the reactor at a reaction mixture temperature of not greater than about 80xc2x0 C., preferably at a temperature of about 50xc2x0 C. to 80xc2x0 C. The acid is added in those instances wherein the triazine charged does not contain at least 1.5% by weight of benzoguanamine and/or acetoguanamine. It should be noted that in this low temperature acid catalyst method, the aldehyde need not be charged after the other ingredients are charged: The reaction mixture is then heated at a temperature of at least 100xc2x0 C. to about 160xc2x0 C. and preferably about 100 to about 140xc2x0 C. until the reaction of phenol in the reaction medium is substantially complete.
The High Temperature Acid Catalyst Method
In the case of the high temperature acid catalyst method, only about half of the aldehyde is charged initially. The acid catalyst will have a pK acidity of about 0.5 to 3.8 in a quantity of about 0.2% to about 2% based preferably about 0.7% to 2% when the acid is formic and about 0.3% to 1% when the acid is oxalic or trifluoroacetic. The quantity of acid is based on the weight of phenol charged to the reaction mixture. A mixture of the phenol, acid and aldehyde will have a pH of less than 2.5 and preferably less than 2 when measured by the procedure shown in Table 10 hereinafter. The initial heating for reaction of the aldehyde is at a temperature of about 70xc2x0 C. to about 110xc2x0 C. and preferably about 80xc2x0 C. to 105xc2x0 C. It is preferred that the aldehyde be added in this initial heating in portions such as about 2 to 4 portions. After the reaction mixture is substantially free of aldehyde, the reaction mixture is heated at a temperature and time sufficient to prevent gelation of the reaction mixture on subsequent addition of the remaining aldehyde. Thus, the temperature is raised to at least about 120xc2x0 C. such as that of about 120xc2x0 C. to about 160xc2x0 C. but preferably from about 120xc2x0 C. to abut 140xc2x0 C. for about 0.5 to 2.5 hours. After this heating step and cooling of the reaction mixture to about 110xc2x0 C. or less such as about 80xc2x0 C. to 110xc2x0 C. the remainder of aldehyde is added and the reaction mixture heated at a temperature of above about 120xc2x0 C., such as from about 120xc2x0 C. to about 160xc2x0 until the reaction of phenol in the reaction mixture is substantially complete.
In both the low temperature acid catalyst method and the high temperature acid catalyst method, after the reaction mixture is substantially free of the initial aldehyde charge, the reaction mixture is heated to a temperature and time sufficient to prevent gelation of the reaction mixture such as on the subsequent addition of the remaining aldehyde in the high temperature acid catalyst method. The time and temperature for this can vary. Thus, in the case of the low temperature acid catalyst method, gelation has been prevented by heating in the presence of added acid at a temperature of about 100xc2x0 C. to 140xc2x0 C. for about one to four hours. In the case of the high temperature acid catalyst method, gelation has been prevented by heating to a temperature of about 120xc2x0 C. to 160xc2x0 C. for about 0.5 to 2.5 hours.
Since phenol is charged in excess to the reaction mixture, a substantial quantity of phenol is distilled out of the reactor. The T-P-A condensate of this invention will incorporate therein about 52% by weight of phenolic residue when the aldehyde to triazine molar ratio is about 2.2 and about 67% by weight of phenolic residue when the aldehyde to triazine molar ratio is about 3.5. The point at which the phenol is substantially completely reacted is arrived when the quantity of free phenol in the reactor remains substantially the same, i.e., additional phenol is not being incorporated into the T-P-A condensate.
A low melt viscosity condensate can be prepared when benzoguanamine and/or acetoguanamine are co-reacted with the melamine. The melt viscosity of such condensate can be well below 2,000 cps and even substantially less than 1000 cps or 600 cps at 175xc2x0 C.
After the substantial complete reaction of the phenol with the intermediate condensate and formation of the T-P-A condensate of this invention, any water which has not distilled out and unreacted phenol are removed from the reaction mixture so that the product is substantially free of water, e.g. less than about 1% and preferably less than about 1.5% by weight, and contains less than about 2% by weight of phenol.
Without wishing to be held to any theory of operation, at the lower temperatures e.g. temperatures of less than 100xc2x0 C., it appears that the principal reaction is methylolation of the triazine with the aldehyde. In such low temperature methylolation the phenol acts principally as a diluent in the reaction mixture and as a solvent for the intermediate methylolated triazine. At the higher temperatures, e.g., above about 100 or 110xc2x0 C. the methylolated triazine and/or melamine to melamine condensate reacts with the phenol and phenolation takes place. Again not wishing to he held to any theory of operation, the heating step, in those methods wherein it is performed after the initial methylolation, appears to cause rearrangement of the intermediate melamine to melamine condensate, so as to free up methylene groups to react with the phenol as well as inhibiting gelation of an intermediate condensate. It is also believed that the addition of acid in the low basicity amine catalyst method after the reaction mixture is substantially free of aldehyde causes rearrangement of an intermediate condensate so as to avoid gelation or excessively high viscosity of the T-P-A condensate on the subsequent heating of the reaction mixture for the reaction of the phenol or completion of phenol reaction in the reaction medium.
The P-T-A condensate of this invention can be further reacted with additional formaldehyde, e.g., 5 to 15%, based on the weight of the initial amount of formaldehyde in order to raise the glass transition temperature of cured compositions of the T-P-A condensate and an epoxy resin.
Removal of Water and Free Phenol
Water can be removed from the reaction mixture by distillation. Whatever water is not removed during such distillations, can be removed after completion of the reactions at temperatures of about 150xc2x0 C. to 160xc2x0 C. and whatever water remains is removed when the excess phenol i.e., free or unreacted phenol, is removed from the reaction mixture by conventional techniques such as that used for removal of phenol from other novolac resins such as by raising the temperature from about 160xc2x0 C. to about 190xc2x0 C. together with increasing the vacuum to about 29 inches of mercury. Steam sparging with or without vacuum at such temperatures can also be used to remove phenol in the product, particularly to achieve free-phenol levels of not more than 2% and particularly levels of less than 0.5%.
The Triazine-Phenol-Aldehyde Condensate
The condensate of this invention will: contain from about 15% to 24% of nitrogen, preferably about 17% to 23% of nitrogen based on the weight of the condensate; have a melt viscosity of not more than about 2,000 cps at 175xc2x0 C. and preferably not more than 1,000 cps at 175xc2x0 C.; and have a solubility of at least 80% by weight and preferably 85% by weight of the condensate as measured by the 90:10 methanol:water method at 25xc2x0 C. or a soluble/insoluble ratio of at least 2.8 as measured by the 90:10 methanol: water method at 25xc2x0 C., after substantially all of the free water has been removed, e.g., less than about 1% and preferably less than 0.5% of water remains, and the free phenol content is not more than about 2%. Such condensate contains from about 55% to about 65% by weight of phenolic residue incorporated in the condensate when the triazine is melamine, the phenol is phenol itself and the aldehyde is formaldehyde. For a given A/T (aldehyde/triazine) molar ratio, the amount of phenolic residue incorporated in the condensate, relative to when the triazine is melamine and the phenol is phenol itself will decrease when the triazine is acetoguanamine or benzoguanamine, and will also decrease when the aldehyde is other than formaldehyde but will increase when the phenol includes a meta-substituted phenol. Increasing the A/T molar ratio will increase the phenolic residue whereas decreasing this ratio will decrease the phenolic residue. Thus, the phenolic residue incorporated in the condensate of this invention will typically vary from about 52% to about 67% by weight of the condensate.
After removal of the unreacted (free) phenol from the reaction mixture, the free phenol content of the T-P-A condensate of this invention should be less than about 2% and particularly less than about 0.5% by weight of the condensate.
When benzoguanamine and/or acetoguanamine are co-condensed with the melamine in the preparation of the T-P-A condensate of this invention, the melt viscosity of the condensate is significantly reduced.
The T-P-A condensate of this invention has good solubility in organic solvents. Thus the condensate of this invention has a solubility in methanol and MEK (methyl ethyl ketone) of up to 50% solids and in some cases with MEK (Ex 4 and 6 of Table 1) and 1-methoxy-2-propanol solutions having 70% solids can be prepared. The T-P-A condensate of this invention is thermoplastic.
Mixture of T-P-A Condensate and Benzoguanamine and/or Acetoguanamine
The mere physical admixture of small quantities of benzoguanamine or acetoguanamine, e.g., about 0.5 to 20% by weight based on the weight of the T-P-A condensate, and preferably about 5 to about 15% together with the T-P-A condensate, significantly lowers the melt viscosity of the mixture. This is particularly surprising since mixing melamine with the T-P-A condensate causes an increase in the melt viscosity of the mixture. Another advantage of the physical blend is that the nitrogen content is increased relative to the T-P-A condensate. This same phenomenon is attained when benzoguanamine and/or acetoguanamine are physically admixed with other T-P-A condensates, e.g., those of U.S. Pat. No. 5,955,184 of September 1999; U.S. Pat. No. 5,939,515 of August 1999; U.S. Pat. No. 5,322,915 of June 1994; U.S. Pat. No. 4,611,020 of September 1986; as well as European patent 877,040 of Nov. 11, 1998 which is assigned to Dainippon Ink and Chemicals, all of which patents are incorporated herein in their entirety by reference. Benzoguanamine and acetoguanamine can also be mixed with T-P-A condensates for curing of epoxy resin compositions.
Epoxy Compositions Derived From T-P-A Condensates
The T-P-A condensates are useful as curing agents for epoxy resins and as intermediates in epoxy compositions. Glycidylated T-P-A condensate can be made by known methods, i.e., by reaction of the T-P-A condensate with excess epichlorohydrin in the presence of an alkali. Isolation is preferably performed below 100xc2x0 C. as there may be a tendency to self-crosslink.
The Epoxy Compositions
The epoxy resins used in making the flame retardant compositions and laminates of this invention will typically have WPE values of about 190 to about 10,000 and preferably about 190 to about 500. Illustrative of the epoxy resins, there can be mentioned those of diglycidyl ether resins, such as those having the above mentioned WPE values, prepared by contacting a dihydroxy compound with an excess of epichlorohydrin in the presence of an alkali metal hydroxide wherein the dihydroxy compound can be: bisphenol A; brominated bisphenol A; bisphenol F; resorcinol; neopentyl glycol; cyclohexanedimethanol, and the like; and mixtures thereof. Such resins are also referred to as being based on or derived from the dihydroxy compound involved, e.g. bisphenol A. Also, such conventional epoxy resin can be that of: epoxy phenol novolacs; epoxy cresol novolacs, particularly glycidyl ethers of an o-cresol/formaldehyde novolacs; aromatic glycidyl amine resins such as triglycidyl-p-amino phenol; N,N,Nxe2x80x2,Nxe2x80x2-tetraglycidyl-4,4xe2x80x2-diaminodiphenyl methane; glycidyl ethers of a phenolic novolac; poly(glycidylated) copolymers of glycidyl methacrylate wherein the comonomer includes unsaturated compounds such as acrylates, methacrylates and styrene; and mixtures of the various conventional epoxy resins. Non-glycidylated epoxy resins may also be employed. Examples of such non-glycidylated epoxy resins include: limonene dioxide (weight per epoxy of 85); vinyl cyclohexene dioxide; divinyl benzene dioxide; 5-vinyl-2-norbornene dioxide (weight per epoxy of 76); 1,5-heptadiene dioxide; 1,7-octadiene dioxide. The non-glycidylated epoxy compounds are preferably used in conjunction with glycidylated epoxy resins and are also useful as diluents.
Epoxy curing accelerators are used in the epoxy compositions in a quantity sufficient to accelerate the cure of the epoxy resin. Generally, such quantity is from about 0.05 to 0.5 parts based on 100 parts of the base epoxy resin and particularly about 0.1 to 0.2 parts. Such accelerators include 2-methylimidazole, 2-ethyl-4-methylimidazole, amines such as 2,4,6-tris(dimethylaminomethyl)phenol and benzyldimethylamine, and organophosphorus compounds such as tributylphosphine and triphenylphosphine.
Compositions of this invention when used in electronic applications such as laminates for the production of printed circuit boards will typically comprise the following composition based on 100 parts of an epoxy resin:
(a) about 0-30 parts of phenolic-formaldehyde novolac;
(b) about 30-60 parts of the T-P-A condensate of this invention; and
(c) optionally, an epoxy curing accelerator.
The T-P-A condensate of this invention can be used alone as both the curing agent and to impart flame-retardant properties to the epoxy resin. Alternatively, the T-P-A condensate can be used together with one or more conventional epoxy resin curing agents and/or flame-retardant agents.
A variety of curing agents well known in the art can be used together with the T-P-A condensate of this invention in curing the epoxy resin. They include but are not limited to aromatic amines, polyamidoamines; polyamides; dicyandiamide; phenolic-formaldehyde novolacs; melamine-formaldehyde resins; melamine-phenolic-formaldehyde resins; and benzoguanamine-phenolic-formaldehyde resins.
Reactive diluents may also be present in the epoxy compositions to lower viscosity and improve handling characteristics. Examples of reactive diluents include neopentylglycol diglycidyl ether; butanediol diglycidyl ether; resorcinol diglycidyl ether; and cyclohexane dimethanol diglycidyl ether.
When phenolic novolacs are used as curing agents a catalyst (accelerator) is generally employed and may be selected from tertiary organic amines such as 2-alkylimidazoles; benzyldimethylamine; and phosphines such as triphenylphosphine and mixtures thereof.
The phenolic novolac curing agents are condensation products of a phenol with an aldehyde or ketone wherein the phenolic monomer can be selected from phenol itself, cresols, xylenols, resorcinol, bisphenol-A, paraphenyl phenol, naphthol, and mixtures thereof. Substituents for the phenolic monomers include hydroxy, alkyl of 1 to 4 carbon atoms, alkoxy of 1 to 4 carbon atoms as well as phenyl. Particularly preferred curing agents are the phenol-formaldehyde novolacs, e.g., wherein the phenol is phenol itself, and ortho-cresol-formaldehyde novolacs having a molecular weight of about 600 to 5,000 and preferably about 1,000 to 5,000. Illustrative of the aldehydes for preparation of the phenolic novolac curing agents there can be mentioned formaldehyde, acetaldehyde, benzaldehyde and hydroxybenzaldehyde. Illustrative of ketones for preparation of the phenolic novolac curing agents there can be mentioned acetone, hydroxyacetophenone, and methyl ethyl ketone.
A wide variety of solvents may be used in the epoxy compositions of this invention, including halogenated solvents, ketones, alcohols, glycol ethers, glycol acetates, N,N-dimethylformamide. The latter is particularly useful when dicyandiamide is used as curing agent. Ketones include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone.
Laminates of the Epoxy Resin Compositions
The laminates of this invention are conventional laminates containing a reinforcing agent such as glass cloth, and a cured resinous matrix comprising an epoxy resin and a T-P-A condensate of this invention as curing agent and flame-retardant alone or together with other curing agents and/or flame retardant agents for the epoxy resin. The laminates of this invention will comprise the reinforcing agent together with the cured epoxy compositions mentioned hereinabove.
The structure of the laminates of this invention are the same as those of conventional laminates containing a reinforcing agent such as glass cloth, and a resinous matrix comprising an epoxy resin and a curing agent for the epoxy resin.
The laminates of this invention will generally contain about 40% to 80% by weight of resinous matrix material and about 20% to 60% by weight of reinforcing material such as glass cloth.
Conventional laminating techniques can be used in making the laminates of this invention such as the wet or dry-lay-up techniques. Multiple layers of resin impregnated reinforcing material, upon curing, make up the laminate.
The pressure used in making the laminates can vary from the contact pressure of applying a laminated lining to a tank wall to the high pressure, e.g., 1,000 psi or more, used in the manufacture of electrical insulation sheets. The temperature used in making the laminates can vary over a wide range such as that of about room temperature to over 210xc2x0 C.
The laminate can be prepared at room temperature or by heating under pressure a layer comprising at least one sheet of prepreg comprising an epoxy resin as impregnate. The pressure used in making the laminates can vary from the contact pressure of applying a laminated lining to a tank wall to the high pressure, e.g., 1,000 psi or more, used in the manufacture of electrical insulation sheets. The temperature used in making the laminates can vary over a wide range such as that of about room temperature to over 210xc2x0 C. The use of a solvent in the laminate compositions is optional. Conventional laminating techniques can be used in making the laminates of this invention, e.g., such as the wet or dry-lay-up techniques.
Reinforcing fibers or fabrics of reinforcing fibers for use in laminates include glass fibers and mats; carbon and graphite fibers, cellulosic paper, fibrous polyamide sheets, fibrous quartz sheets, woven fibrous glass cloth, unwoven fibrous glass mat, and the like. The epoxy resin composition will be impregnated in the reinforcing fibers or fabrics or the interstices formed from of such fibers or fabrics. Fillers such as quartz powdered, mica, talc, calcium carbonate and the like may also be added to the resinous matrix in the manufacture of the laminate.
Phosphorus containing additives for epoxy formulations with the triazine-phenol-aldehyde condensate of this invention include: elemental red phosphorus; phosphorus and phosphoric acids; triphenyl phosphine; triphenyl phosphine oxide; cyclic and linear phosphazines such as various phenoxyphosphazene compounds; tris(2-hydroxyphenyl)-phosphine oxide; 9,10-dihydro-9-oxa-10(2,5-dioxotetrahydro-3-furanylmethyl)-10-phosphphaphenanthrene-10-oxide; melamine phosphate; melamine cyanurate; non-halogenated phosphorus compounds in U.S. Pat. No. 3,702,878; U.S. Pat. No. 5,481,017; U.S. Pat. No. 4,086,206; and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite (Ultranox 626 by GE Specialty Chemicals of Parkersburg , W.Va.) The quantity of the phosphorus containing additive can vary from about one percent to ten percent based on the weight of the T-P-A additive.
The weight average molecular weight (Mw) and number average molecular weight (Mn) herein are measured using size exclusion gel permeation chromatography (SEC) and phenolic compounds and polystyrene standards. The sample molecular weight to be measured is prepared as follows: the sample is dissolved in tetrahydrofuran and the solution is run through a gel permeation chromatograph. Any free phenolic in the sample is excluded from calculation of molecular weight. SEC as a measure of molecular weight is highly dependant on the hydrodynamic volume of the material in solvent. Highly branched or polycyclic materials tend to give lower values than molecular weights determined by other means such as vapor phase osmometry (VPO).
In order that those skilled in the art may more fully understand the invention presented herein, the following procedures and examples are set forth. Unless otherwise indicated, the following units of measurement and definitions apply in this application: all parts and percentages are by weight; temperatures are in degrees centigrade (0xc2x0 C.); use of oxalic acid is as the dihydrate; and readings of vacuum are in inches of mercury.
All heating steps in the examples herein were conducted under a nitrogen atmosphere, unless otherwise specified.
A 4 ounce jar with stir bar is charged with 10.0 g (gram(s)) condensate and 27 g of methanol. The jar is capped and the mixture is stirred at ambient temperature until the condensate is dissolved or until no further dissolution occurs (typically one-half to about 2 hours). To the stirred mixture is added dropwise 3.0 g of deionized water. The mixture is further stirred at least 1 hour and then allowed to settle unstirred. Twenty (20.0) g of clear liquor is transferred to an aluminum weighing cup. Solvent is largely evaporated and further drying occurs in an oven at 60xc2x0 C. for about 2 hours. Essentially complete drying is attained followed by heating 2 hours at 100xc2x0 C. under 29 to 29.25 inches of mercury vacuum. The residue, if any, represents the soluble fraction from the 20 g of solution. Any insoluble fraction left in the jar is obtained by removing all the remaining clear liquor and drying the insolubles as described above. In instances where insolubles are a free flowing powder, centrifugation is employed to separate clear solution from solid. Time to reach equilibrium solubility can be accelerated by warming (e.g., 35xc2x0 C.) the stirred methanol-condensate mixture and adding the water dropwise. Stirring for another 1 hour and then allowing the temperature to reach ambient. The solubility percentage is determined by dividing the insoluble portion in grams by ten due to the 10 gram sample to get the insoluble percentage and then subtracting the insoluble percentage from 100 to arrive at the solubility percentage of the condensate involved. Thus, from Table 5 the solubility percentage for Durite SD 1732 (a novolac resin of Borden Chemical, Inc of Columbus, Ohio) is 100% since there are no insolubles whereas the solubility of Example 25 is 82%.
Viscosities, at 175xc2x0 C., were determined with a cone and plate viscometer from Research Equipment (London) Ltd. Number 40 and 100 spindles were used depending on the viscosity reading. A factor multiplier of 300 was used for the Number 40 spindle and a factor multiplier of 800 was used for the of 100 spindle values shown from digital readout. For example, a digital reading of 20 obtained with a #40 cone spindle would be multiplied by 300 to give a viscosity value of 600 cps.